Colorectal cancer (CRC) can result from uncontrolled cell growth in the colon or rectum (parts of the large intestine), or in the appendix. CRC can develop from a colon polyp. A colon polyp typically comprises a benign clump of cells that forms on the lining of the large intestine or rectum. While many colon polyps are non-malignant, a polyp can develop into an adenoma. Colorectal adenomas can then grow into advanced colorectal adenomas, which can then develop into CRC.
Colorectal cancer is a leading cause of cancer-related deaths in the United States with over 142, 820 diagnosed cases and over 50,000 deaths in 2013. According to a 2011 study, there are an estimated 1.2 million diagnoses per year and 600,000 deaths worldwide. CRC is one of the most preventable cancers given its typically slow progression from early stages to metastatic disease and available tools for its diagnosis, but it is one of the least prevented cancers. This is at least partly due to the poor compliance with available screening by patients due to the invasive or unpleasant nature of the current screening tests.
The risk of developing CRC increases with age. Ninety percent of new cases and 93% of deaths occur in people age 50 and older. During their 60s, men have a 10-fold increased risk of developing CRC compared to their 40s. Regular screening allows for the removal of advanced colorectal adenomas or precancerous polyps and detection of early stage cancer, which is the key factor in the effective treatment of the disease.
The survival rate for patients diagnosed with CRC is highly dependent on when it is caught. CRC usually progresses through four stages, defined as Stage I through Stage IV. Stages I and II are local stages, during which aberrant cell growth is confined to the colon or rectum. Stage III is a regional stage, meaning the cancer has spread to the surrounding tissue but remains local. Stage IV is distal and indicates that the cancer has spread throughout the other organs of the body, most commonly the liver or lungs. It is estimated that the five-year survival rate is over 90% for those patients who were diagnosed with Stage I CRC, compared to 13% for a Stage IV diagnosis. If caught early, CRC is typically treated by surgical removal of the cancer. After the cancer spreads, surgical removal of the cancer is typically followed by chemotherapy
Colonoscopy and sigmoidoscopy remain the gold standard for detecting colon cancer. However, the highly invasive nature and the expense of these exams contribute to low acceptance from the population. Furthermore, such highly invasive procedures expose subjects to risk of complications such as infection.
The most common non-invasive test for colorectal cancer is the fecal occult blood test (“FOBT”). Unfortunately, in addition to its high false-positive rate, the sensitivity of the FOBT remains around 50% and may have less sensitivity for detection of early stage CRC. Numerous serum markers, such as carcinoembryonic antigen (“CEA”), carbohydrate antigen 19-9, and lipid-associated sialic acid, have been investigated in colorectal cancer. However, their low sensitivity has induced the American Society of Clinical Oncology to state that none can be recommended for screening and diagnosis, and that their use should be limited to post-surgery surveillance.
Because of the significantly increased chance of survival if CRC is detected early in the disease progression, CRC is one of three cancers for which the American Cancer Society, or ACS, recommends routine screening (breast and cervical cancer are the others). In the United States, screening for CRC is currently recommended by the ACS and the U.S. Preventative Services Task Force, or USPSTF, for all men and women aged 50-75 using fecal occult blood testing, or FOBT, which is a fecal test, or one of two procedures: colonoscopy or sigmoidoscopy. Despite the benefits of routine screening on improving five-year survival rates if CRC is diagnosed early, the rate of screening compliance is low due in part to the limitations of existing solutions.